Offset printing apparatus



2 Sheets-Sheet l A 'ITORNE YS.

A. W. STEPHENSON OFFSET PRINTING APPARATUS Filed March 50, 1931 May 2, 1933.

/lllllllllilflllllnlllf llnlillllll May 2,y 1933.

A; W. STEPHENSON oFFsE T PRINTING APPARATUS Filed March 30, 1.931

2 s-nets-sneei ATTORNEYS.

Patented May 2, 1933 UNITED STATES PATENT oFFlcE* ARLINGTON W. STEPHENSON, OF SAN FRANCISCO, CALIFORNIA, ASSIG-NOR, BY' MESNE 0F SAN FRANCISCO, CALIFORNIA, A CORPORA- ASSIGNMENTS, TO THE FAX COMPANY TION OF CALIFORNIA OFFSET PRINTING- APPARATUS Application led March 30, 1931. Serial No. 526,219.

This invention relates to that form of printing known as offset printing in whlch the design on the printing plate is first prlnted on a rubber blanket from which the imprint is offset to the paper.

The objects of my invention are to provlde means for adapting the fiat printing plate to the offset method of printin Also such means which may be applie to a platen printing press, also which will permit the use of fine screen half-tone platesior printing on coarse-grained paper with the same clear detail as in printing on high grade coated ,stock and without distorting the surface of the paper, particularly at the edges of the plate, and also which will permit the press to give the full number of impressions per hour for which the ordinary platen printlng press is designed to deliver. Other objects ofthe invention will appear in the following description.

Before describing the apparatus, attentlon is called to the fact that heretofore in typographic printing a definite relation has necessarily existedbetween half-tone plates and the nature of the paper on `which the halftone is to be printed in order to economically produce prints having the prolper qualities. A fine screen half-tone proper y printed on a high quality hof enameled paper gives the most nearly perfect result, but if printed on a poor grade of paper, the half-tone will fill up, smut, and produce very vpoor results. Heretofore the line and other very coarse screen half-tones have been found to give the best results on newspaper stock, 85 to 100 line screen half-tones for low grade of book paper, 120 to 133 line screen half-tones for medium grade of book paper, uncoated stock and lower grades of coated stock, and halftones finer than 133 line has necessitated the use of highest grades of coated stock, while 200, 300 and 400 line screen half-tones are not ordinarily used for commercial work, but are confined almost exclusively to the :reproduction of scientific subjects due to the slowness of production on account of the necessity for cleaning the plates at very frequent intervals. t

` With my invention fitted on a platen press, and using a planographic plate in which the printing surface bears an image 1n mercury amalgamated onto the printing surface to function as a repellant for the printing ink of a roller rolled thereover, and whlc'h ink adheres to the non-amalgamated portions of the plate 200 line screen half-tone plates produce perfect sharply defined images on any kind of paper, coated or uncoated, -of any grade, soft or hard, and on rough cover stock without markingk the paper along the edges of the plate, so as to give a plate sunk effect.. In using my apparatus on a platen printing press and with the planographic plate as above mentions more than 25,000 uniform lmpressions from a 200 line screen halftone have been made on rough cover stock, high grade coated stock and newspaper stock at an average speed of 1500 impressions an hour without cleaning the plate or adjusting the apparatus, without smudging the prints on any'of the different papers, without loss of detail in the prints and without any noticeable wear whatsoever on the plates. y

Brlefiy described, my apparatus comprises a flat rectangular plate herein termed impress1on plate mounted on a platen press in a manner vinterposed between platen of the press with the opposite flat faces of the plate in a plane parallel to the respective surfaces of the form and platen so that the impression plate will be squeezed between the form and the platen when the press is closed. The impression plate is covered on both sides with a rubber blanket and when the press is closed upon it the inked image on the mercury printing plate is printed on the confronting rubber-covered face of the impression plate, while at the same time the opposite side of the impression plate is pressed against a piece of paper lying onv the platen. The impression plate is pivotally mounted at its side edges between a pair of spaced posts or arms, so asto revolve on a horizontal axis and in a manner to be carried outward from the form and the platen as the press opens after the printing operathe form and -along the line as soon as there is sufficient clearance between the form and the platen, thereby presenting the inked impression on the rubber blanket in confronting relation to the platen for offsetting to the paper the next time the press is closed and at the same time presenting the opposite uninked side of the rubber blanket in confronting relation to the printing plate for receiving the next inked impression therefrom upon the 'next closing of the press.

The paper is fed to the platen in the usual manner, but with each impression the print is made on the paper from the rubber blanket at one side of the impression frame while at the same time the blanket on the opposite face of the frame receives a fresh ink impression'from the printing plate, the impression plate carrying the blankets revolving 180o after each impression as stated.

While my device may be adapted to any style of platen printing press, the apparatus indicated in the drawing is shown as mounted on a platen press of the sliding platen type just so much of the common press elements being shown in full line as to make it clear and understandable.

In the drawings Figpl is a fragmentary sectional side view of portion of a platen press showing my apparatus in place and the press open, a portion of the press being in dotted lines.

Fig. 2 is an enlarged view of my apparatus as seen from the line 2-2 of Fig. 1.

Fig. 3 is a side view of Fig. 2.

Fig. 4 is an enlarged sectional 4-4 of Fig. 2. Fig. 5 is an enlarged sectional view taken view taken along the line 5-5 of Fig. 2.

Fig. 6 is an enlarged v1ew of a portion of Fig. 2 as seen from the line 6-6 thereof.

Fig. 7 is an enlarged sectional view taken along the line 7f-7 of Fig. 2.

Fig. 8 is an `enlarged sectional view taken along the line 8-8 of Fig. 2. j

Fig. 9 is an enlarged de tail of Fig. 1 as seen from the line 9-9 thereof.

Fig. 1() is an optional cross section of the impression plate.

In detail, 1 designates in dotted line the frame of a platen printing press of the sliding platen type with the platen 2 in open position for feeding, and in the closing of this press the platen is tion parallel with and then drawn against the printing plate 3 mounted on bed 4 of the press, upon oper'ation of crank 5, this printing position of the platen being indicatedin dotted line at 2 and carried out by any of a number of platen press constructions not involved in the present invention.

Ordinarily, in order to retain the paper against the platen when the platen assumes the position indicated at 2', a frisket frame 6 comprising a horizontal bar with a horizontal slot extending from end to end there- `side edges through tending trunnion shafts 11 journaled in the,

first brought to a posiedge thereof,

of is pivotally mounted atits opposite ends adjacent the forward corners of the platen as at 7 and two or three upstanding parallel frisket lingers or grippers not shown, are bolted against the forward face of the frisket frame with bolts extendin through the slot therein, and these frisket ngers are brought against the face of the paper to be printed on opposite sides of the plate 3 when the platen is vertical in the well understood manner, thus firmly holding the paper fiat against the platen as the platenv moves toward the plate 3 for making the printing impression, all of 'which is standard structure and well known in presses of this type.

' In using my apparatus the Vfrisket fingers' are omitted from the frisket frame and a pair' of vertically extending parallel bracket arms 8 are substituted therefor and are bolted at their lower ends as at 9 against the front face of the frisket frame 6, best shown in Fig. 2.

` etween arms 8 is mounted the impression plate 10 preferably made of aluminum, and which plate is of flat rectangular form revolvable on a horizontal axis at opposite means of outwardly exarms 8 and projectin beyond the outer sides of said arms. The vs afts are provided with fixed lianges 12l secured .to the edges of the impressionframe by screws or otherwise.

On the projecting portions of the shafts respectively are a pair of spiral dental clutch members 13, 13. The inner clutch member 13 is free to rotate on the shaft while the outer clutch member 13 is slidably splined on the shaft, the shaft preferably being square outward of member 13 as indicated in Fig. 5, and the member 13 having a square axial opening therethrough. The adjacent faces of clutch members 13, 13 are provided with complementary spiral ratchet teeth which are normally forced into engagement with .each other by a coil spring 14 carried on the shaft outward of clutch member 13 by a washer and pin as indicated.

The inner clutch member 13 carries spur 15 around its periphery, which engage the teeth of .a rack 22 slidably retained against each of the armsS and parallel thereto, said arms being grooved as at 16 to form guides for the racks, retaining plates 17 being secured against the arms 8 and extending over the open sides of -each groove and'across the outer sides ofthe racks to hold them in place.

The upper ends of the racks terminate adjacent the upper ends of arms 8 and are connected to each other at their upper ends by a horizontally extending rod 18, which rod normally extends across the front margin of the impression plate 10 adjacent the upper the upper ends of arms 8 being slotted as at 19 (Fig. 6) to permit the rod 18 to pass across between the racks and to member 23 and serve as a brace or stop for the rod 18 when it is in the slot.

The guiding grooves 16 terminate above the lower ends of arms 8 and racks 22 extend downward in them to a point just above the bolts 9 which secure the arms 8 to thefrisket frame 6. Extending inwardlyl toward each other from the lower ends of the racks are short horizontal arms .20 which arms pass through the lower ends of elongated vertical slots 21 in the lower ends of arms 8 respectively, the lower edges of the horizontal arms 20 resting against the lower ends of the slots. After passing through slots 21 the arms 2O extend vertically downward as at 20 to a point below the frisket frame and then horizontally as at 23, which latter run forms the connecting piece between the vertical runs 22, thus forming a yoke member 20,' 20', and 23 connecting the two racks 22 Midway of the run 23 of the yoke is a fiat depending piece 24 formed integral with provided with an elongated vertical slot 25.

A pair of spaced downwardly extending guide plates 26 are bolted as at 27 to the frisket frame 6, and which plates extend over the front face of the horizontal run 23 of the yoke.

In vthe structure described it is evident that the yoke connecting the racks 22 is free to move upward carrying the racks and rod 18 with it but is held against further downward movement by the ends of slots 21, the clutch teeth of clutches 13, 13 being arranged so that upward movement of the racks turns clutch members 13 therewith without turning clutch members 13', but latter clutch members engage with members 13 for turning on a downward movement of the racks only,

and turn the impression frame 10 completely over.

In order to automatically effect an upward movement of the yoke and racks when the press opens, a pair of stationary cams 28 with horizontal upper surfaces are bolted to opposite sides of the press frame 1 -in the lower end of a cutoutv ortion provided in the press frame for perm tting free movement of the platen and frisket frame into the vertical printing position as indicated in dotted lines at 2 in Fig. 1. v

When the frisket frame, carrying the complete structure, as already described moves with the platen to assume the position indicated at 2 in Fig. 1, the lower edges ofthe outer ends of the horizontal run 23 of the yoke engage against the horizontal upper faces of cams 28 before the extreme downward movement of the frisket frame is reached, and as'the action of the press continues to move the frisket frame downward,

the yoke and mechanisms secured thereto are forced upward so that the rod 18 connecting the upper ends of the racks is clear of the upper edge of the revolvable plate 10 as at 18 in Fig. 2. Upon a subsequent downward movement ofthe yoke, it is evident from the structure already described lthat the spiral or ratchet clutches 13, 1'3 will engage and effect a 180? revolution of impresslon plate 10'and the rod 18 will be loweredinto its position in front of` plate 10.

Means is provided for lowering the rack bars and yoke, and this comprises a pair of coil tension springs 29 positioned adjacent the front faces of arms 8 respectively, the upper ends of thesprings being secured to rod 18 at their upper ends and at their lower ends each to the arms 8 respectively as and at best indicated in Fig. 2.

In order to retain the impression plate 10 against turning until the platen and form are sufiiciently separated, a pair of leaf springs 30 are secured at 30 at their lower ends by bolts or rivets to the rear face' of 'the vertical run 22- of the yoke and extend upward so as'to slide over the rear face of plate I10 adjacent its side edges when the yoke is forced v upwardupon the closing action-of the press as described.

time the platen has moved away from the bed and form a suicient distance to enable a free 180 revolution of the frame 10, the yoke will have been pulled down by springs 29 sutliciently far to permit plate 10 to be released from leaf springs 30 by overcoming the resistance of the leaf springs, and will quickly effect a half turn of the plate which turn is limited by rod 18 which automatically descends into the slots in the upper ends -of arms 8 respectively in front of the plate and in which position further revolution of plate 10 is impossible. The catches 31 in the sides of arms 8 adjacent the lower corners of therplate also function to retain the plate 10 against rebounding out of position between arms 8 after the half revolution of the plate is completed, as the plate -would otherwise have a tendency to do upon striking rod 18 along its upper margin. b.

In view of the positive and powerful action of a platen press, it is essential to also provide means positively actuated by the movement of the press itself, instead of plac-V ing-full reliance on coilsprings 29, to turn the plate 10, as serious damage\to the device the upper margin ofand press might result were the plate 10 not to make a full halfyturn and to this end a strap iron bracket 32 is bolted at one end to cross brace 33 of the press frame,^which brace or similar member found in most presses of this character extends between the sides of the press beneath the platen carriage. Bracket 32' extends inward towards the bed of the press and is provided with a bearing 32 at its inner end in which is mounted a short shaft 34 extending horizontally and transversely of the bracket. Shaft 34 carries at one end an upwardly extending hook 35 which has a straight downwardly extending shank 36, the shank extending through the shaft and a distance below it. A pair of collars are pinned to the shaft 34 on opposite sides of the bearing 32 as indicated in Fig. 9 to prevent longitudinal displacement of the shaft, yet to permit it to freely rotate therein.

Around the shaft and between the bearing 32 and the hook 35 I provide a torsion spring 37, one end of which bears against the bracket and the opposite end against the hook 35 and is adapted to force the hook in a direction P away from the press bed. Opposing Athe force of spring 37 is a `coil tension spring 38 secured at one end to the end of shank 36 and to the other end of the spring -is attached the end of a smallcable 39 the other end of the cable being secured by abolt to the longitudinally extending throw off arm 40 of the platen carriage as indicated in Fig. l.

In operation, when the platen carriage has moved away from the bed of the press a suiicient distanceto enable the frame 10 to turn, and just after the frame has turned, hook 35 is pulled forward against the force of torsion spring 37 under the superior force of spring 38 and enters slot 25 of piece`24 of the yoke and engages the piece 25 at the lower end of the slot, and as the platen continues to recede from the bed, raising the yoke, the yoke member and racks secured theretoare positively pulled downward to forcibly complete the half turn of plate 10 should the springs 29 fail for any reason to carry out their function. In the reverse motion of the platen, namely, toward the press bed, the tensionon spring 38 is relieved and the hook moves out of slot 25 to dotted position 35 in Fig. l, so as to permit the yoke to descend to its full downward limit for resettingthe clutch members for a succeeding turn of plate 10. The use of springs 29 to turn the plate 10 is preferable to effect a uniform turning of the plate, since it is obvious that were the hook 35 depended upon to perform the full function of turning the plate, the turning force would vary with the speed of the press, at times not effecting as rapid an' action as would be desired and at other times the force would be stronger than desired and cause excessive Wear on the parts. The hook 35 merely provides extra or dual means for insuring a complete turn ofthe impression plate, although it would operate alone without the springs 29.

I-Iook 35 is adjustable in its motion by tightening or releasing the tension of spring 38.

The impression plate 10 of my device is recessed on its opposite flat faces as best shown in Fig. 4, the face of the margin o f the plate around the recesses being flushl with the rear faces of arms 8 irrespective of which face of rthe plate is turned to face the rear side.

Preparatory to printing by use of my device, a filler or pad comprising several cards 42 of coated stock and a blotter or several blotters 43 are first placed in the recesses in the plate faces in which theV filler is adapted to snugly fit with the cards 42 at the bottom of the recess and the blotter on top, the blotter extending above the face of the margin of the plate. Preferably the pad or filler is gummed along an edgeto prevent the cards and blotters shifting relative to each other and to make a unitary filler of diferent paer stock.

With the illers in place, one in each recess on opposite sides of the impression plate, a firm countersunk impression of the printing plate is made in each of the fillers by closing the press to printing position with the printing plate 3 (on its block 3') locked in the chase 4 on the bed 4 of the press. After making these impressions which leave countersunk depressions in the fillers the size of the printing plate, a piece of hand-coated cardboard 44 or a piece of stencil board of slightly smaller dimensions than the printing plate is placed in each of the depressions made in the filler, leaving arfree or open mar gin 48 between the edges of the board 44 and the edge of the depression made by the printing plate A the face of the board being above the face of the blotter. The frame 10 with its fillers prepared as described are then removed from between the arms 8 by turning the plate 10 to the dotted position l0 in Fig. l in which position the screws mounting the shafts l1 to t-hev plate are exposed and are easily removed. An endless resilient rubber blanket 45 is then slipped over one end of the plate 10, fillers, and boards 44, so as to leave the side margins of the plate free for leaf springs 30 to slide thereagainst as already described. With the blanket in place the fillers and boards 44 are firmly held in place by friction.

The plate 10 with the filler and blanket in place forms a unit which is then remounted on bearings 11 and is ready for receiving inked impressions on the rubber blanket from -the printing plate for offsetting to the paper.

- However, it is preferable to also cover the platen with a resllient rubber blanket as indicated at 46, on which is laid the paper to serting the card 44 therein to raise the portion of the filler to receive the inked impression from the plate, eliminates the necessity for underlaying thev back of the printing plate to insure an evenly inked impression, and also prevents the edges of the printing plate from `cutting into the rubber blanket during the printing operation, since the edgesl of the plate overhang the edges of the card 44, as best indicated in dotted line in Fig. 4 and they are therefore entirely relieved of pressure.

Instead of making the impression plate as shown in Fig. 4 wherein it is a built-up series of members with a central sheet or web 10 of metal, the whole thing may consist of a light metal open frame holding a series of padding sheets as shown in Fig. 10 wherein the margins of the plate are made of two overlapping thin metal angle strips 49, 50 held together as by screws 5I, the outer strips being provided with lugs 52 carrying the pivot shafts 53 on which the whole impression plate revolves. Within the frame are layers of paddingor pressure receiving material comprising a central sheet of heavy stencil board 54 on opposite sides of which are sheets of rm rubber 55 preferably reinforced with duck, then comes thin stencil board 56, then sheets of coated cardboard stock 57, then relief padding 58 of thin cardboard, and iinally the oset rubber blanket 45 which wraps around the whole assembly as described for Fig. 4 to thus form my impression plate, though it really has a yielding center. This compound impression plate is more yielding than the plate of Fig..4, though if in the latter ligure the web 10 be very thin or not made integral with the outer frame 10 it is about the same, though in somerespects I find the floating or yielding center type of impression plate to work best.

From the above it will be seen that my use or'l the words impression plate is to be construed broadly as covering any modifications, whether fiexible, rigid, built-up or otherwise.

In making the printing plates for printing by my process and with the device` described, the area on the plate carrying the image is as indicated at'47 in Fig. 4, the extreme edges .of the plate and margin being left blank and covered with mercury to repel the ink.

It is obvious to anyone skilled in the art that certain parts ofv my device may be changed according to the nature of the press on which it is used. It is also obvious that it may be used in printing ordinary half-tone plates, or other cuts, as it is not limited to use with mercury planographic plates, but it consists broadly in an automatic reversal apparatus for carrying out oiset printing from iat forms on platen'presses of any description, and any modifications or use falling within the spirit of the invention are intended to be covered in my ap-pended claims.

I claim 1. In combination withA a platen type of printing press, a flat oii'set impression plate positioned between the printing form and the press platen, means mounting said impression plate'for revolution to present opposite sides in succession to the form and the platen, and dual means operated in synchrony with the press movements for revolving the plate a .half turn between impressions, one of said dual means being resiliently operated and lthe other positively operated, the latter arranged to take eect upon failure of the former.

2. In combination with a platen type of printing press, an offset impression plate positioned between the printing form and the press platen, means mounting saidims pression plate for revolution to present opposite sides in succession to the form and the platen, the means mounting said impression plate including an attachment wheresoy by it is wholly supported from the frisket frame of the press, and means operated in synchrony with the press movements for revolving the plate between impressions.

3. In combination with a platen type of printing press, an oil'set impression plate positioned between the printing form and the press platen, means mounting said impression plate for revolution to present opposite sides in. succession to the form and the platen, and means operated in synchrony with the press movements for revolving the plate between impressions, the means mounting the impression plate comprising a pair of vertically positioned supporting arms, horizontal pivots between the plate and arms whereby the plate may be revolved between the arms, and the means for revolving the plate comprising resilient power means for. urging the plate to revolve on its pivot, stop means limiting the revolution of the plate, and means for intermittently actuating said resilient power means.

'4. In combination with a platen type' of printing press, an oii'set impression plate positioned between the printing form and the press platen, means mounting said impression plate for revolution to present opposite sides in succession tothe form and the platen, and means operated in synchrony with the press movements for revolving the plate between impressions, the means mounting the impression plate comprising a pair of vertically positioned supporting arms, horizontal pivots between the plate and arms whereby the plate may be revolved between the arms, the means for revolving the late comprising springs for urging the p ate to revolve, movable stop means limiting the revolution of the plate, and means actuated by the press movements intermittently actuating said springs and moving said stop means.

5. Oiset prlnting apparatus comprising a at offset impression plate, supports at opposite edges of said plate, means pivoting the plate to the supports for revolution of the plate, a revolvable clutch associated with one of the pivots, a rack bar slidabl;7 supported on one of said supports engaging said clutch, a spring arranged for sliding the rack bar, and means for tensioning the spring to cause revolution of said clutch and plate.

6. Oii'set printing apparatus comprising a flat ofset impression plate, supports at opposite edges of said plate, means pivoting the plate to the supports for revolution of the plate, a revolvable clutch associated with one of the pivots, a rack bar slidably supported on one of said supports engaging said clutch, a spring arranged for sliding the rack bar, means for tensioning the spring to cause revolution of said clutch and plate, and means for stopping said plate at each half turn.

7. In printingI apparatus of the character described, a at impression plate provided on opposite sides with a flexib e sheet rubber blanket formed in an endless band tensioned around the plate.

8. In printing apparatus of the character described, a at impression plate provided on opposite sides with a iexible sheet rubber blanket and padding under the blanket arranged `to register with, but of 'lesser size than the printing form.

ARLINGTON W. STEPHENSON. 

